1. Field of the Invention
The present invention relates to an internal structure of a power driven hammer drill, and more specifically to an intermediate housing disposed between a gear housing and a motor housing.
2. Description of the Related Art
A power driven hammer drill generally includes an intermediate housing arranged between a gear housing and a motor housing as disclosed in Japanese Utility Model Laying-Open Gazette No. 61-172786 by the applicant of the present invention. FIG. 9 schematically shows a typical example of such conventional power driven hammer drills. The hammer drill includes an intermediate housing 204 positioned between a gear housing 202 and a motor housing 203. The intermediate housing 204 consists of a bearing member 241 for supporting an armature shaft 206 of a motor 205 and an intermediate shaft 207 and separating a piston cylinder 232 from the motor 205, and a cylindrical piston housing member 242 protruded from the bearing member 241 for supporting a rotating tool holder 230 and a reciprocating piston cylinder 232.
The intermediate housing is required to have sufficient strength and durability, and is generally composed of a metal such as aluminum as disclosed in UK Patent Application GB 2085345.
In the conventional metal intermediate housing described above, the bearing member 241 and the piston housing member 242 are separately manufactured and assembled later, which increases both the cost and labor and makes the hammer drill undesirably heavy. Metal outer faces 204a of the intermediate housing 204 exposed to the atmosphere may cause electric shocks.
Another structure of an intermediate housing is disclosed in UK Patent Application GB 2085345, in which a bearing member and a piston housing member are integrally composed of aluminum. The metal intermediate housing of this structure also makes the hammer drill undesirably heavy to prevent smooth operation of the hammer drill, and requires excessive works for making bores and holes, which increase the manufacturing cost and labor. Inside the aluminum housing member is generally covered with iron or another metal to improve the durability, which further increases the manufacturing cost. The metal intermediate housing is accommodated in a plastic housing to prevent possible electric shocks, which enlarges the outer diameter of the hammer drill.